This application is a national stage application of PCT/GB00/00268 which was published in English under publication number WO 00/44851 oil Aug. 3, 2001.
The present invention relates to electroluminescent materials which can emit light in the ultra-violet region of the spectrum and devices made using such materials.
Materials which emit light when an electric current is passed through them are well known and used in a wide range of display applications and organic polymers have been proposed as useful in electroluminescent devices, but using these polymers it is not possible to obtain pure colours, they are expensive to make and have a relatively low efficiency.
Another compound which has been proposed is aluminium quinolate, but this requires dopants to be used to obtain a range of colours and has a relatively low efficiency.
In an article in Chemistry letters pp 657-660, 1990 Kido et al disclosed that a terbium (III) acetyl acetonate complex was green electroluminescent and in an article in Applied Physics letters 65 (17) Oct. 24, 1994 Kido et al disclosed that a europium (III) triphenylene diamine complexes was red electroluminescent but these were unstable in atmospheric conditions and difficult to produce as films.
The complexes disclosed in these articles had a relatively low photoluminescent efficiency and were only able to produce green or red light and other colours could not be produced.
Patent Applications WO 98/58037 and WO 98/55561 disclose electroluminescent materials which emit light in the visible spectrum and disclose electroluminescent devices incorporating these materials.
The wavelength of the emitted light from an organo metallic complex which is an electroluminescent material depends on the metal or metals and the ligands.
In general the shorter the wavelength of the emitted light the harder it is to obtain effective electroluminescent materials and in particular electroluminescent materials which emit light in the ultra-violet region of the spectrum have hitherto not been possible to produce.
An electroluminescent material which can emit ultra-violet light would have a range of applications and would enable there to be a source of ultra-violet light without the need for high temperature or complex high energy or vacuum equipment and so could replace such sources of ultra-violet light.
For example, there are devices and displays etc. where ultra-violet light is used to excite other materials to cause these other materials to fluoresce in the visible spectrum.
For example, there are devices and displays etc. where ultra-violet light is used to excite other materials to cause these other materials to fluoresce in the visible spectrum.
We have now devised organo-metallic complexes which can emit ultra-violet light.
According to the invention there is provided an electroluminescent material which emits light in the ultra-violet region of the spectrum which comprises an organic metallic complex of a transition metal, lanthanide or actinide and a polyamine ligand.
The preferred metal is gadolinium in the III state.
Preferred ligands are ethylene diamine tetramine EDTA, DCTA, DTPA and TTHA.
The structural formulae of these compounds in the acetic acid form are shown below. 
The organo metallic complexes can be made by the reaction of gadolinium chloride with an alkali metal salt of the amine e.g. the sodium salt, for EDTA the reaction is
GdCl3+Na4(EDTA)xe2x86x92Na+[Gd(EDTA)]xe2x88x92
For the other polyamine the corresponding alkali metal salt is used. With polyamines which arc more than tri-functional e.g. EDTA, DCTA, DTPA, TTHA the complexes can be in the form of a salt e.g. an alkali metal salt and can be used in this form. Alternatively a transition metal, lanthanide or actinide salt e.g. Ln*[Ln(EDTA)]3 where Ln and Ln* is a transition metal, lanthanide or actinide and preferably a lanthanide e.g. Gd, Sm, Eu, Tb, Dy, etc.
Particularly preferred mixed complexes are the gadolinium complexes e.g. Gd[Eu(EDTA)]3.
It has surprisingly been found that the lanthanide salts of the organo-metallic complexes exhibit a different electroluminescent spectrum than mixed organ-metallic complexes.
The mixed lanthanide salts can be made by reacting a lanthanide chloride with a lanthanide polyamine complex.
The materials of the present invention can be incorporated into electroluminescent devices which emit ultra-violet light and the invention include such electroluminescent devices.
The materials of the present invention can be incorporated into electroluminescenlt devices which emit ultra-violet light and the invention include such electroluminescent devices.